Fabric flaw detector



Jan. 7, 1964 w. a. KLEIN ETAL FABRIC FLAW DETECTOR 4 Sheets-Sheet 1 Filed Sept. 2, 1960 Jan. 7, 1964 w. G. KLEIN ETAL FABRIC FLAW DETECTOR 4 Sheets-Sheet 2 Filed Sept. 2, 1960 lllllnl IIIIIIIJ "w n A 1964 w. e. KLEIN ETAL 3,116,621

FABRIC FLAW DETECTOR Filed Sept. 2, 1960 4 Sheets-Sheet 3 Jan. 7, 1964 w. s. KLEIN ETAL FABRIC FLAW DETECTOR 4 Sheets-Sheet 4 Filed Sept. 2, 1960 I l I HIIIIIIHIIIIIHIIIIIIIIIIIIJI|||lllllllllllll Fl] I L ll /UlIHHIIIlllllllllllllllllllHIIIIlllllllill United States Patent 3,116,621 FABRIC FLAW DETECTOR William G. Klein, Newton Center, and Allen K. Swanson, Walpole, Mass., assignors to Fabric Research Laborattllries, Inc, Dedham, Mass, a corporation of Massac usetts Filed Sept. 2, 1960, Ser. No. 53,654

Claims. (Cl. 66-166) This invention relates to a method and apparatus for detecting flaws in textile fabrics and more particularly to a method and apparatus which employs the photoelectric detection means and is especially adapted for the detection of flaws, such as holes and runs, in tubular knitted fabric materials.

It is desirable to provide means for inspecting textile fabric materials automatically in order that flaws therein may be detected in an expeditious and labor-saving manner. This detection may take place as the fabric is being formed thereby minimizing the manufacture of defective fabric and enabling the prompt correction of improper machine operation, or at a later stage, for example, just prior to the garment making operation.

However, certain conditions involved therein make difficult the provision of a suitable automatic fabric flaw detection system. An example of a particularly troublesome flaw is the run (a reduced thread density) which is knitted continuously due to a defective needle until that produced by the starting and stopping of associated machines, line voltage fluctuations, mechanical shocks and vibrations. In addition, particles of dust and lint also may actutate that type of photoelectric stop motions when the device is designed to have a sensitivity sufiicient to detect the absence of a few threads. If the sensitivity of the device is reduced, however, major defects in the fabric are too frequently not detected. Among the other problems related to fabric flaw detection systems are those due to the fact that the fabric may gradually stretch or contract as it moves, thereby increasing the light transmission. In addition, it is frequently ditlicult to position the detection apparatus adjacent the knitting machine or other fabrication device so that the flaw may be detected promptly. The problems involved in the fabric flaw detection become greatly accentuated where tubular fabric is involved as that fabric is conventionally handled in collapsed double thickness form.

Accordingly, it is an object of the invention to provide an improved method of textile fabric flaw detection which enables accurate sensing of fabric flaws in a variety of operational situations and under diverse environmental conditions.

Another object of the invention is to provide an improved method of textile fabric flaw detection in which the fabric is moved relative to a sensing device at a known and constant speed and error signals produced by the 'ice sensing device are detected according to .predetermined frequency relationships.

Still another object of this invention is to provide an improved flaw detection apparatus utilizing a photoelectric sensing means which is suitable to use for detecting a variety of fabric flaws including both a complete ab sence of threads and a partial absence of threads.

Another object of the invention is to provide a fabric flaw detection apparatus which is sensitive to the rate of change of the fabric sensing signal rather than the magnitude thereof.

Another object of the invention is to provide an improved method and apparatus for fabric flaw detection which is particularly adapted for use with tubular knitted fabrics.

Another object of the invention is to provide a photoelectric flaw detection device particularly adapted to the detection of runs in knitted fabrics and suitable for mounting in intimate association with the knitting components of a tubular fabric knitting machine.

Still another object of the invention is to provide an improved method of fabric flaw detection utilizing photoelectric sensing means which is substantially insensitive to changes in the environment surrounding the apparatus.

In accordance with the principles of the invention, the fabric to be inspected is moved relative to a straight edge disposed generally perpendicular to the direction of movement of the fabric relative thereto at a substantially constant and predetermined velocity. The fabric is inspected as it moves past the straight edge and upon the sensing of a fabric flaw a signal which contains a known frequency component is produced. That frequency component is detected and utilized to appropriately indicate the existence of the flaw.

In the preferred embodiments of apparatus incorporating principles of the invention there is provided a photoelectric sensing means which is adapted to be disposed adjacent the fabric to be inspected and arranged so that complete absence of thread elements, when sensed, produces a sudden marked change in the signal output of the sensing means and the detecting apparatus responds to this sudden change. The detection circuitry is preferably adjusted to have maximum sensitivity to the principal frequency component of the signal change produced by the flaw. Upon detection of such a frequency compo nent, the detection apparatus is adapted to operate a stop motion or otherwise appropriately signal the existence of the flaw. In the run detection systems there is a similar sudden change in the magnitude of the signal produced by the photoelectric sensing means. However, this change is not as great as occasioned by the existence of a hole. As this flaw is one of a continuous nature, the sensing apparatus, as applied to a tubular fabric flaw detection system, is disposed sothat the fabricmoves along a generally helical path past the sensing head. In this manner the run will pass the sensing head repeatedly and an integrating arrangement is employed in the detecting circuitry so that the stop motion or signaling device is actuated only after the run has been sensed a number of times.

In the preferred embodiments the photoelectric sens ing head is mounted immediately adjacent the tube of fabric, and the fabric is moved past the sensing head in a direction generally perpendicular to the slit aperture therein. A light source mounted within the sensing head is positioned so that the light falls on the slit aperture past which the fabric moves and is normally reflected from the fabric onto one or more photocells. When a fiaw is sensed, the amount of light reflected is suddenly reduced, producing an error-signal having a predetermined frequency component which is related to the velocity of the fabric moving past the slit in the sensing head. In the hole detector utilized in conjunction with the laying up operation of tubular fabrics, the fabric is passed over a spreader structure of substantially nonrefiective nature and a plurality of photoelectric sensing means are disposed in a row about the spreader so that the entire width of each surface may be sensed, while in the preferred form of run detector used in conjunction with the knitting operation, a single photoelectric sensing unit is employed.

The length of the slit in the run detector system is disposed parallel to the direction of a run and hence the run is sensed over the entire length of the slit, while in the hole detector system, the slit is aligned perpendicular to the run direction and is not designed to respond to such a flaw. However, those flaws, in the normal course of events, would have been picked up by the run detector.

The detecting circuitry in each device, being responsive to a carefully chosen interval of frequencies rather than the magnitude of the output signal, has substantial advantages over prior art flaw detection systems. Among the problems involved is the fact that the signals produced by the photoelectric cell will normally include a variety of frequency components which may be produced by a gradually changing density of the cloth, for example, and although these frequency ranges include frequency components different from those produced by the Sensing of a flaw, their magnitude is sufficient to mask the flaw signal unless some type of discrimination is employed. With the use of an appropriately tuned filter circuit, preferably band pass in nature, the frequencies produced by the flaws are attenuated to a smaller extent than the other frequencies. This detection and discrimination also enables the elimination of the spurious responses such as those due to line voltage conditions, mechanical shocks, vibrations of the frequencies of the associated machines and electrical transient conditions.

The frequency of the signal produced by the flaw is, in general, a function of (1) the speed of the cloth relative to the detector slit, and (2) the width of that slit. The sensing system may be reponsive to the frequency produced by the rise time of the flaw signal or the dwell time of the signal, the former being a function only of the relative speed of the cloth and the latter being a function also of the width of the slit. The rise time principle is employed in the preferred type of run detector which is tuned to a frequency of about 200 cycles per second and which utilizes a single shock mounted sensing unit. The dwell time principle is employed in the layup or hole detector apparatus as there are certain advantages to the lower frequency in this case. Among these are the facts that the frequency of vibrations produced by the layup machine is in the order of 200 cycles per second and that it is more difficult to fabricate an appropriately shock mounted unit as a much larger number of sensing cells are employed. Accordingly, the detecting circuitry is tuned to a frequency range i th vicinity of 30 cycles per second.

Thus the sensing apparatus associated with the flaw detector is tuned to the strongest frequency component of the flaw as determined empirically.

The preferred embodiment of the hole detector is particularly suited for use in conjunction with the layup operation just prior to the garment cutting process wherein the fabric produced may be rapidly examined for holes and when such flaws are detected the associ ated apparatus actuated so that the defective portion may be removed from the fabric materials; and the preferred embodiment of the run detector is particularly suited for location in close cooperation with a knitting machine or similar device.

The fabric flaw detection system according to the invention thus provides a method of automatically, reliably and accurately sensing fabric flaws which is suitable for incorporation into mass production systems.

Other objects and advantages of the invention will be seen as the following description of preferred embodiments thereof progresses in conjunction with the drawings, in which:

FIG. 1 is a fragmentary vertical sectional view of a conventional tubular fabric knitting machine provided with a photosensitive run detection apparatus constructed in accordance with principles of the invention;

FIG. 2 is a perspective view of the detector head utilized with the knitting machine of FIG. 1 and the casing which houses the associated electronic apparatus;

FIG. 3 is a sectional view through the detector head and associated fabric taken along the line 33 of FIG. 1;

FIG. 4 is a sectional view through the detector head and associated fabric taken along the line 4-4 of FIG. 3;

FIG. 5 is a diagrammatic front view of the detector head and fabric illustrating a typical movement of a point on the inspected fabric relative to the detector head;

FIG. 6 is a schematic diagram of the electronic circuitry associated with the run detector head shown in FIGS. 15;

FIG. 7 is a perspective view of a tubular fabric hole detection apparatus constructed according to principles of the invention;

FIG. 8 is a sectional view of the tubular fabric hole detection apparatus of FIG. 7 taken along the line 88 of FIG. 7;

FIG. 9 is a perspective view of the hole detection apparatus of FIG. 7 with the fabric removed from the supporting member and showing only a single detector head; and

FIG. 10 is a schematic diagram of a portion of the electronic circuitry associated with the embodiment of the invention shown in FIGS. 79.

A sensing apparatus adapted to detect runs in tubular knitted textile fabrics is shown in conjunction with a conventional tubular knitting machine in FIG. 1 of the drawings. This specific type of knitting machine is shown for illustrative purposes only, and it will be understood that flaw detection devices constructed in accordance with principles of the invention may be used with a Wide variety of devices. The illustrated knitting machine 10' includes a needle cylinder 12 which is driven in rotary motion by a set of miter gears (not shown) and which carries a plurality of needles 14. Surrounding the needle cylinder 12 at the top is a radially-slotted guide annulus 16 for the web holders 18. Axially disposed above the cylinder within the circle of the latch needles 14 is the dial 20 for the usual welting instrumentalities which are actuated by cams (not shown) on a superimposed plate 22 stationarily supported by a bracket 24 on the latch guard ring 26 of the machine. The shaft 28 of the welting dial 20 extends upward through a bearing box 30 mounted on bracket 24. The dial shaft 28 is driven in unison with the needle cylinder 12 through a pair of bevel gears 32, 34, from a short horizontal shaft 3 6.

A pair of cooperative take-up rolls 33, 40 are transversely disposed within the upper part of the needle cylinder at a level somewhat below the knock-over ledge level of the web holders 18. The rolls 38, 40 may have coverings of comparatively soft rubber or the like so that the fabric will not be marred by them and are rotatably mounted on shafts 42, 44. The opposite ends of the shafts are engaged in axially aligned apertures in an annular supporting tube 46. The tube 46 rests on top of the hub of the driving gear and is connected to the needle cylinder 12 by a key and accordingly is caused to rotate therewith. Offset bevel gear pinions, not shown, on the opposite ends of the take-up rolls 38, 40 mesh with a ring of similar gear teeth 48 disposed below the take-up rolls 'in the tube 46.

In operation, the tube of fabric 54) knitted by the needles is worked downward below the needles into a somewhat conical configuration and is led through the take-up rolls 38, 4t). The knitted fabric itself is being constantly rotated and the take-up rolls are likewise rotated by the coaction of the ring gear 48 with the bevel gears on the take-up roll shafts. The take-up rolls are carried in rotation with the tube 46 and the ring gear 4% is driven independently thereof so that the take-up rolls are driven 'to pull the knitted fabric 50 through the nip thereof in a compressed double thickness.

A detector head housing 52 is mounted within'the tube of newly knitted fabric immediately below the dial 20.

The housings for the photosensitive element of the flaw detector and its associated electronic circuitry are shown in FIG. 2. A photoelectric sensing device is mounted in the semi-cylindrical detector head housing 52, the curved surface 53 which has a vertical elongated aperture or slit 54 positioned therein. In this embodiment, the width of the slit is approximately /8 inch and it is two inches in length. The detector head housing 52 is mounted relative to the fabric being knitted on arm 55 as shown in FIG. 1, and is connected by means of a cable 56 to the electronic circuitry housing or cabinet 57. Shaft 23 of the welting dial 20 is hollow and a tube 58 extends through the hollow shaft into the area below the dial 2%,

the upper portion of the tube 58 being supported from the bracket 24 by an arm 59. The detector head housing 52 is pivotally mounted by a friction joint 60 on arm 55 and is normally held in proper sensing position by spring 61. The offset friction joint 60 normally holds the head 52 in proper position but on the occurrence of a pressotf (a large hole in the fabric) it is pivoted over the to gle point and the head is snapped by the spring 61 out of the path of the fabric. In addition, the mounting structure makes the proper aligning of the detector head during start up operations easier and more convenient. Mounted on the front panel of the cabinet 57 is a meter 62, a reset button 64, an on-off switch 66 and a signal light 68. On the rear panel of the circuitry cabinet is a terminal strip, not shown, to which the stop motion circuitry may be connected.

The mounting of the photosensitive element within the detector head housing may be best understood with reference to FIGS. 3 and 4. As pointed out above, the detector housing has a curved wall 53 in which is positioned the slit 54. A polished transparent window 69 of Plexiglas or similar transparent material is secured across the slit to exclude lint from the interior of the housing. Mounted generally parallel to the bottom wall of the detector head housing is a support plate 7i and supported by this plate opposite the slit 54 is the photosensitive element 72 which is, in the preferred embodiment, two Hoffman 1.20c shock-mounted, series connected self-generating silicon photo-cells. Disposed to either side of this photosensitive element and slightly to the rear thereof on the support plate are lamps '74, 76. Shield portions 78, positioned on either side of the photosensitive element prevent the light rays emanating from the lamps from falling directly onto the photocells. The interior of the housing is non-reflective and thus a very low intensity of light normally falls upon the photosensitive surfaces in the absence of light transmitted via the slit. Electrical connections for the photosensitive material and for the lamps are led through appropriate insulators 82, $4 and are formed into the lead cable 56 which passes through the rear wall of the detector head housing.

In operation, the detector housing is positioned such that its cylindrical surface 53 abuts a surface of the web of fabric that has just been knitted with the slit 54 accurately aligned with the wales of the fabric. In the course of knitting, a point on the knitted fabric moves with substantially constant velocity and follows a generaily helical path downward as indicated by the arrow 86 in FIG. 5. The length of the slit 54 is preferably determined so that a substantial portion of the fabric passes across the slit. Light from the lamps 74, 76 passes through the slit and falls on the fabric which is passing in front of the slit. A certain portion of the light is reflected from the threads of the fabric onto the photocells 72, this portion of the light being a function of the type of fabric that is passing the slit at that time. If the fabric is properly constructed, a relatively constant amount of light is reflected and the photocells produce a signal indicative of this condition. However, if the knitting is imperfect as, for example, where a run has been formed, the amount of light which is reflected to the photosensitive surface will be suddenly reduced as the run enters the slit area and a changed signal level, indicative of that fact, will be passed over cable 56. The leading portion of the signal includes a frequency component which is a function of the speed that the fabric is moving relative to the slit. This frequency component is detected by associated control circuitry.

A schematic diagram of the control circuitry used in conjunction with these sensing head elements is shown in FIG. 6. This control circuitry is adapted "to operate a stop motion or other suitable signaling apparatus which is connected to the circuitry by means of a terminal strip located on the back panel of the cabinet 57. The circuitry is designed to detect and pass signals in a comparatively narrow band of frequencies in the vicinity of 200 cycles per second, the frequency of the signal produced on detection of a flaw in this combination of equip rnents. The detected signal is produced, in the preferred embodiment, by the reduction in light reflected when a portion of a run first enters the slit, although of course the circuitry could be easily modified to detect the signal change produced when the flaw leaves the slit, for example.

With reference to FIG. 6, the detector head housing 52 is grounded by lead 9%. p The photosensitive cells 72 are loaded by'a 10K ohm resistor 92 and the signal therefrom is coupled into the pre-amplifier circuit 94 by a l microfarad capacitor 96. The RC time constant of the input I ircuit thus is short enough so that the signal increments suchas those resulting from slow changes in fabric reflection characteristics, for example, are not passed 'to the pro-amplifier. When a run or other similar flaw occurs, however, the amount of reflected light is suddenly and markedly reduced and this change of comparatively large magnitude is readily passed by the coupling capacitor 96 to the pre-amplifier circuit94. The pre-amplifying circuit includes two PNP transistors 98,100, type 2N43, which are connected in grounded emitter configuration. The signal .past the capacitor is amplified by the first transistor 93 and then further amplified'by the second transistor 100. A shunting capacitor 102 of 0.5 microfarad capacity and a 2.5 millihenry choke 104'are utilized to eliminate the unwanted high frequency transients substantially above 200 cycles per second. The amplified signal from the preamplifier 94 is then passed through a limiter circuit containing a diode 112, type 1N46l, biased to pass only these signals above a certain amplitude. The potentiometer 116 (limit adjust), associated with the pre-amplifier circuit 94, is provided so that the amplitude of the preamplifier output signal resulting from the detection of a run may be adjusted to be in the same range as the threshold signal that will be passed by the limiter circuit 110.

The signal passed by the diode limiter circuit is coupled by an 0.01 microfarad capacitor 118 to the base of the grounded collector NPN transistor 120, type 2N78, which serves as an impedance matching device for the pulse amplifier stage 122. This amplifier stage also contains two grounded emitter PNP transistors 124, 126, type 2N43. A potentiometer 128 connected to the collector of the first transistor 124, serves as a gain control device and the signal passed by the potentiometer is coupled by a 5 microfarad capacitor 130 to the base of the second stage transistor 126 of the pulse amplifier. The transistor 126 further amplifies the pulse and it is coupled by capacitor 132 to the integrator circuit 134.

The integrator circuit includes two diodes 136, 138 connected in series. The terminal of a 5 microfarad capacitor 140 is connected to the junction between the diodes, the other terminal thereof being grounded. The resistor 142, connected to the junction between the diodes provides a leakage path of fairly long time duration. It will be seen that the diode 136 is poled to permit capacitor 140 to be charged but to block discharge therethrough and the diode 138 is biased to pass only a signal above a predetermined magnitude. A potentiometer 144, connected between the cathode of diode 136 and the junction, provides means for adjusting the amount of charge that can be built up on the capacitor 140 from any given pulse signal. The proper setting of the charge rate adjust potentiometer 144 is governed by the speed of the machine on which the detector is used and the type of textile fabric material being inspected. This circuitry permits the capacitor to accumulate a charge resulting from several signal changes, each of comparatively low magnitude as would occur on each sensing of a run until that flaw is detected several times, for example, while permitting a relatively minor flaw or certain spurious variations of transient nature to pass without operating the associated stop motion. In other words, where the machine is knitting a run, that run will pass the sensing slit repeatedly and a charge will be built up on the capacitor 140 which ultimately overcomes the back bias of the second diode 138 and then a signal is passed by that diode to the relay trip and hold circuitry 146.

The trip and hold circuit includes two NPN transistors 148, 150 which are connected in grounded emitter configuration and a PNP transistor 152. When a signal is passed by the diode 138 to the transistor 148, that transistor conducts to amplify the signal and apply it to the relay 154, thus operating it and changing the setting of the contacts associated with the terminal strip 156. This circuit is extremely stable and operates independently of substantial temperature and voltage variations. When the transistor 148 is turned on and the relay is operated, transistors 150 and 152 are also turned on. The turn-on of transistor 152 causes the voltage on the base of the transistor 150 to rise so that its emitter is more negative than its base and that transistor conducts, thus supplying a holding voltage to the coil of relay 154. This holding voltage is maintained on the relay coil until the reset button 64, as seen in FIG. 2, is depressed. That operation opens the emitter circuit of transistor 150, turning that transistor off, and also discharges the capacitor 140, thus restoring the control circuitry and permitting another detecting op eration to be commenced.

Associated with the circuitry is a full wave rectifier circuit 158 which converts the 120 volt AC. power supplied over lines 160, 162 to direct current for supplying the requisite current to the incandescent lamps 74, 76 mounted in the detector head 52 and the necessary power for the operation of the electronic circuitry. A conventional vacuum tube voltmeter circuit 164 is also provided which includes the meter 62.

In operation, the sensing head is preferably mounted on the knitting machine at approximately a angle to the knitted fabric with the slit 54 disposed generally perpendicularly to the direction of movement of the fabric. The head should be pressed into the fabric so that there is a slight tension across the front of the head thus ensuring proper contact of the fabric with the cylindrical surface 53. After the detecting circuitry is warmed up, the knitting machine is turned on and with the cloth or fabric running normally there should be little or no reading on the meter 62, indicating no signal from the amplifying circuits. When a run or other flaw occurs, a charge on capacitor is built up and that charge build-up is indicated by the meter 62. The charge build-up due to a run should require several revolutions of the fabric to obtain a three-quarter full scale reading on the meter. The relay 154 then will be actuated and the connected stop motion operated to turn off the knitting machine. The number of revolutions of fabric required to actuate the stop motion may be controlled by adjustment of the charge rate potentiometer 144. The gain control potentiometer 128 may also be varied as necessary. If, with the cloth running normally, no run or other defect occurs, but accumulation of charge on capacitor 140 is indicated by meter 62, the setting of the limit adjust potentiometer 116 may be adjusted so that the signal output of the pre-amplifier 94 is reduced.

A second embodiment of the invention is shown in FIGS. 7-9. This embodiment of the invention is particularly designed for the inspection of tubular fabric in the cutting room during the layup operation rather than contemporaneously with the fabric making process. In this embodiment there are two rows 170, 172 of photosensitive elements positioned on opposite sides of the fabric to be inspected. Each row of photosensitive elements is mounted in a separate sensing head 174, 176 respectively and also positioned within each sensing head is a D0. operated fluorescent lamp 178, 180 which is mounted so that no light therefrom falls directly on the photosensitive surfaces. The photosensitive elements are mounted in two parallel rows and interposed between them is a spreader structure 182 over which the tubular fabric is adapted to be drawn. The spreader structure includes a nonreflecting black surface structure 184. As shown in FIGS. 7-9, the framework of the spreader structure is supported on two fabric gripping rolls 188, that are adapted to pull fabric 192 past the sensing heads. This framework includes a peripheral tubular member 194 and two horizontally mounted spaced spreader bars 196, 198, and is supported on the fabric gripping rolls by a set of rollers 200. Mounted within the peripheral member 194 is the black flat surfaced member 184. Positioned on either side of the spreader structure is a guide which is secured to fixed supports 202, 204, and engages the peripheral member in supporting relationship. Each guide includes a grooved roller 206, 208 respectively which is rotatably mounted on an associated arm 210, 212 secured to the associated fixed support. The tubular fabric 192 is passed over the spreader structure and the support rollers and down through the nip of the gripping rolls 188, 190 as shown in FIGS. 7 and 8. A detector head housing 174, 176 is positioned on either side of the peripheral frame structure between the two horizontal spreader members so that the fabric tends to be forced inwardly and is in intimate engagement with the cooperating detector head surfaces.

As shown in FIGS. 8 and 9, in each detector head, there is a horizontal slit 214, 216 which is disposed generally perpendicularly to the direction of movement of fabric therepast. In this embodiment the slit is in the order of /2 inch in width as the primary purpose of this apparatus is for the detection of holes that have a dimension in that order of magnitude. Light from the fiuo- 'rescent lamps is directed onto the slits generally as indicated by the arrows in FIG. 8. Variations in the fabric due to holes or 'siinil'a'r'flaws cause sudden marked reduction in the amount of light reflected onto the photosensitive surfaces of one or more photocells and the resultant change of signal is applied through appropriate associated electrical circuitry'to operate a signaling device.

The associated electrical circuitry is shown in the schematic diagram of FIG. 10. As indicated in that figure, the photocells in each row are connected in four groups and each group including twelve cells connected in series. In this embodiment, there are four pre-amplifier units and associated limiter circuits, two groups of cells being associated with each pre-amplifier unit. Only one preamplifier and limiter circuit is shown in detail in FIG. 10. The frequency to which this circuitry is responsive is in the order of 30 cycles per second. This frequency range was selected in part due to the nature of the flaws being detected, the fact that the associated layup machine had a mechanical vibration frequency in the order of 200 cycles per second and also due to the fact that it is difficult to suitably shock mount the number of photocells utilized in this unit. This frequency is a function of the dwell time (the interval that the hole is in front of the slit) and thus is related to the width of the slit and the speed of the fabric relative thereto.

The output from each group of photocells is connected by a coupling capacitor 218 to the associated pre-amplifier circuit 220 which includes first and second PNP transistor 222 and 224. The pre-amplifier circuitry and the associated diode limiter circuitry 226 is substantially the same as that utilized in the run detector shown in FIGS. 16. Interposed between the two transistors in this embodiment is a low pass filter 228 having a peak response in the range of 30 cycles per second. This filter may be a conventional RC filter circuit with an additional stage of amplification to compensate for lost gain or a series resonant RLC circuit with the output being taken across the resistor thereof as shown in FIG. 10. The output of the limiter is connected to a pulse amplifier circuit 230 similar to that described above only the first transistor of which is shown in FIG. and that circuit is connected directly to a relay trip and hold circuit. (No integrator is necessary as the flaws to be detected are holes rather than length flaw such as runs which may be repetitively sensed.) As indicated above, when the fabric passing in front of the slit has a hole in it, the photocells adjacent that point receive a significantly reduced amount of illumination. The resultant change in output level is amplified by the circuitry, and the associated relay will be operated to signal the detection of the flaw.

Thus, there have been shown and described herein two type of flaw detector systems particularly adapted for inspecting tubular knitted fabrics. One of the disclosed detector systems is adapted to be associated with the knitting machine and the associated circuitry is particularly sensitive to runs while the other detector system is designed for use in the cutting room and is adapted for the detection of holes and similar types of flaws. The preferred embodiments employ a photoelectric sensing apparatus which utilizes light reflected from the fabric and its associated detecting circuitry includes a frequency sensitive unit which eliminates spurious signals produced by sources other than the fiaws. Detector systems employing principles of the invention are reliable in operation and capable of performing rapid and accurate inspections. Although preferred embodiments of the invention have been shown and described, certain modifications thereof will be obvious to those skilled in the art, and it is not intended that the invention be limited thereto or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

We claim:

1. A photosensitive fabric flaw detection apparatus for inspecting tubular fabrics comprising a sensing head, means for moving the fabric to be inspected at a substantially constant and predetermined speed relative to said head and in contact with a surface thereof, said surface having 'a slit therein, the major dimension of said slit being disposed generally perpendicular to the movement of fabric relative to said head, a light source mounted within said head and adapted to illuminate said slit and the fabric passing in front of said slit, a photosensitive device mounted within said head and positioned substantially in alignment with said slit, said device being adapted to sense light reflected from said fabric and to produce a signal representative of the quality thereof, means for preventing light rays from said source from falling directly on said photosensitive device, and means responsive to the signal from said photosensitive device including frequency sensitive means for providing an associated equipment operating signal only when said frequency sensitive means detects a frequency component in the signal from said device indicative of the existence of a fabric flaw.

2. The apparatus as claimed in claim 1 wherein said photosensitive device comprises a plurality of self-generating photocells connected in series and disposed within said sensing head along a line generally parallel to the major dimension of said slit.

3. The apparatus as claimed in claim 1 and further including means for supporting said sensing head in position adjacent and below the top of the needle cylinder of a tubular knitting machine with said slit disposed along a substantially vertical plane so that said fabric is moved past said slit along a generally helical path.

4. The apparatus as claimed in claim 1 and further including a substantially nonreflecting surface positioned on the other side of said fabric opposite said sensing head.

5. The apparatus as claimed in claim 1 wherein said photosensitive means is adapted to be mounted immediately adjacent a knitting machine with said slit being disposed along a substantially vertical line and wherein said fabric is moved past said slot along a generally helical path so that a flaw of continuous nature is repetitively sensed and said signal responsive means further includes an integrator circuit capable of indicating the cumulative effect the signals produced as a result of repeatedly sensed minor fabric flaws, said integrator circuit being adapted to generate an output signal after said photosensitive device has sensed a flaw a plurality of times.

6. A flaw detection apparatus for the inspection of textile fabrics comprising a sensing device adapted to be mounted immediately adjacent a knitting machine, said sensing device including a housing having a slit therein, said housing adapted to be positioned on one side of the fabric with said slit disposed along a substantially vertical line, a light source disposed within said housing for projecting a beam of light through said slit onto said fabric, means for moving said fabric past said slit along a generally helical path at a substantially constant and predetermined speed so that a flaw of continuous nature is repetitively sensed, light sensing means disposed within said housing in a position to sense light reflected from said fabric and to produce a signal representative of a flaw of said fabric, the light sensed by said sensing means and the signal produced thereby varying in accordance with the quality of said fabric, means for detecting the signal produced by said sensing means including means sensitive to a predetermined frequency component of said signal, said predetermined frequency being a function of the speed of said fabric relative to said slit and being produced by the sensing of a flaw in said fabric, and integrating means capable of indicating the cumulative effect of signals produced as a result of the repetitive sensing of a flaw, said integrating means being adapted to generate an error signal indicative of the existence of a flaw when the signal produced by said sensing means References Cited in the file of this patent UNITED STATES PATENTS La Pierre et a1 Jan. 25, 1938 Thomas Apr. 11, 1944 12 Linderman Aug. 14, 1956 Rideout June 7, 1960 Leirner et a1 Dec. 27, 1960 Reip Mar. 28, 1961 Meiners et a1 July 11, 1961 Nickell July 31, 1962 Meiners et a1 Sept. 25, 1962 

1. A PHOTOSENSITIVE FABRIC FLAW DETECTION APPARATUS FOR INSPECTING TUBULAR FABRICS COMPRISING A SENSING HEAD MEANS FOR MOVING THE FABRIC TO BE INSPECTED AT A SUBSTANTIALLY CONSTANT AND PREDETERMINED SPEED RELATIVE TO SAID HEAD AND IN CONTACT WITH A SURFACE THEREOF, SAID SURFACE HAVING A SLIT THEREIN, THE MAJOR DIMENSION OF SAID SLIT BEING DISPOSED GENERALLY PERPENDICULAR TO THE MOVEMENT OF FABRIC RELATIVE TO SAID HEAD, A LIGHT SOURCE MOUNTED WITHIN SAID HEAD AND ADAPTED TO ILLUMINATE SAID SLIT AND THE FABRIC PASSING IN FRONT OF SAID SLIT, A PHOTOSENSITIVE DEVICE MOUNTED WITHIN SAID HEAD AND POSITIONED SUBSTANTIALLY IN ALIGNMENT WITH SAID SLIT, SAID DEVICE BEING ADAPTED TO SENSE LIGHT REFLECTED FROM SAID FABRIC AND TO PRODUCE A SIGNAL REPRESENTATIVE OF THE QUALITY THEREOF, MEANS FOR PREVENTING LIGHT RAYS FROM SAID SOURCE FROM FALLING DIRECTLY ON SAID PHOTOSENSITIVE DEVICE, AND MEANS RESPONSIVE TO THE SIGNAL FROM SAID PHOTOSENSITIVE DEVICE INCLUDING FREQUENCY SENSITIVE MEANS FOR PROVIDING AN ASSOCIATED EQUIPMENT OPERATING SIGNAL ONLY WHEN SAID FREQUENCY SENSITIVE MEANS DETECTS A FREQUENCY COMPONENT IN THE SIGNAL FROM SAID DEVICE INDICATIVE OF THE EXISTENCE OF A FABRIC FLAW. 